1. Field of the Invention
The invention relates to a system for transferring electric energy to a vehicle, in particular to a road automobile or to a track bound vehicle such as a light rail vehicle (e.g. a tram). Examples of track bound vehicles are conventional rail vehicles, mono-rail vehicles, metros and busses (which may be guided on the track by optical means or mechanical means other than rails).
2. Description of Related Art
Track bound vehicles, in particular vehicles for public passenger transport, usually comprise a contactor for mechanically and electrically contacting a line conductor along the track, such as an electric rail or an overhead line. Typically, at least one propulsion motor on board the vehicles is fed with the electrical power from the external track or line and produces mechanic propulsion energy. In addition or alternatively, the transferred energy can be used for operating auxiliary systems of the vehicle. Such auxiliary systems, which do not produce traction of the vehicle, are, for example, lighting systems, heating and/or air conditioning system, the air ventilation and passenger information systems. Not only track-bound vehicles (such as trams), but also road automobiles (for example having four wheels with tyres to drive on a road) can be operated using electric energy.
If continuous electric contact between the travelling vehicle and an electric rail or wire along the route is not desired, electric energy can either be withdrawn from an on-board energy storage or can be received by induction from an arrangement of electric lines of the route.
The transfer of electric energy to the vehicle by induction forms a background of the invention. A route side (primary side) conductor arrangement produces a magnetic field, which is in particular a component of an alternating electromagnetic field. The field is received by a coil (secondary side) on board of the vehicle so that the field produces an electric voltage by induction. The transferred energy may be used for propulsion of the vehicle and/or for other purposes such as providing auxiliary systems of the vehicle (e.g. the heating and ventilating system) with energy.
Generally speaking, the vehicle may be, for example, a vehicle having an electrically operated drive motor. However, the vehicle may also be a vehicle having a hybrid drive system, e.g. a system which can be operated by electric energy or by other energy, such as energy provided using fuel (e.g. natural gas, diesel fuel, petrol or hydrogen).
WO 95/30556 A2 describes a system wherein electric vehicles are supplied with energy from the roadway. The all-electric vehicle has one or more on-board energy storage elements or devices that can be rapidly charged or supplied with energy obtained from an electric current, for example a network of electromechanical batteries. The energy storage elements may be charged while the vehicle is in operation. The charging occurs through a network of power coupling elements, e.g. coils, embedded in the track. Induction coils are located at passenger stops in order to increase passenger safety.
U.S. Pat. No. 4,836,344 discloses an electrical modular roadway system adapted for transmitting power to and controlling inductively coupled vehicles travelling thereon. The system comprises a plurality of elongated, electrically connected inductor modules arranged in an aligned end to end spaced apart order to form a continuous vehicle path. Each module has a magnetic core and power windings which generate a magnetic field extending above the road surface. The modules are embedded in the ground so as to be flush with the roadway surface over which a vehicle can travel. Each module is an elongated structure of uniform width and thickness so that they can be easily fabricated in quantity and readily installed in a roadbed with a minimum of labor and equipment. Each module comprises an iron core around which is wrapped a power winding comprising a series of coils.
Although the electric conductors are arranged immediately above the ground or are buried in the ground, there may be systems or devices below the conductor arrangement and, consequently, electromagnetic compatibility (EMC) requires to keep intensities of electromagnetic fields or magnetic fields small.